This invention is directed to a switch mode power supply for a television receiver. When a switch mode power supply is in a stand-by mode, only a small amount of power is transmitted, that is the switching transistor is periodically electrically driven to be conducting by groups of pulses, i.e. a burst operation. After the television receiver is turned on, an initial, or start-up, mode of operation is initiated which triggers the transition from the stand-by mode to an ON mode. In the ON mode, the power transmitted is raised to the rated value by increasing the operating (on) time of the switching transistor. At the transition from the stand-by mode to the ON mode, which occurs during the start-up operation, there is the danger that, due to unexpected occurrences the switching transistor, is subjected to significant voltages and currents which can damage the transistor.